Provisioning pretender

Being able to grab unused storage from one part of the company and use it in another is a hallmark of thin provisioning and a feature that sets this allocation method apart from a related provisioning strategy -- dynamic volume expansion.

Supported by various operating systems, dynamic volume expansion is an online way of increasing storage volumes as necessary and is a capability often confused with thin provisioning, according to Tony Asaro, an analyst at Enterprise Strategy Group.

"Dynamic volume expansion does not support shrinking the size of a volume," Asaro explained in a recent thin-provisioning report.

Because it does nothing about storage that has been allocated for future use but is idling within an organization, dynamic volume expansion doesn't prevent storage hogging or the tendency among users to overestimate the amount of space needed over a given period of time, Asaro says.

Thin provisioning explained

Sometimes referred to as over provisioning, allocate-on-write or dedicate-on-write technologies, thin-provisioning options let storage buyers avoid tying up entire pools of capacity immediately.

Instead, IT executives can project the entire amount of storage a department will need in the long term but purchase only the minimal capacity that the unit will consume over a shorter period. Enterprise officials then work with vendors to set thresholds that signal when additional capacity is necessary and implement alarms or notifications that indicate when it's time to add more disks to a particular storage pool.

Storage hogging -- or the tendency among users to overestimate the amount of space a specific business unit or project will consume over a given period of time -- is the No. 1 problem thin provisioning seeks to solve. Second is the storage haggling that ensues when CIOs struggle to avoid buying extra storage upfront while knowing that much of the capacity will remain uselessly stranded within the organization.